(a) Field of the Invention
The present invention relates to non-magnetic toner including toner components having different mean grain sizes and, more particularly, to a non-magnetic toner for use in an electrophotography, which is made of a mixture of toner components including particles having no carriers therein and different mean grain sizes.
(b) Description of the Related Art
In an electrophotographic printer using a non-magnetic toner having a single main ingredient without a carrier therein, the toner is generally electrified by rubbing operation using a doctor blade which attaches the toner particles to a developing roller by applying a contact pressure to the toner Such a non-magnetic toner contains a mixture of different toner components having different mean grain sizes. The mean grain size is generally represented in terms of grain diameter measured from the volume of toner particle and the number of toner particles or mean grain diameter measured from the actual size of each particle.
The non-magnetic toner including toner components having mean different grain sizes generally suffers from a difference in electrified charge between a particle having a larger grain size and a particle having a smaller grain size due to the difference in the surface area therebetween. In general, the smaller toner particles are electrified with larger electric charge per unit area compared to the larger toner particles. Thus, the smaller toner particles are attracted more firmly by the developing is roller due to larger mirroring force and accordingly pass by the doctor blade more easily compared to the larger toner particles irrespective of the contact pressure being applied between the doctor blade and the developing roller. As a result, the smaller toner particles are provided to the developer in an amount more than the amount of the larger toner particles in an initial stage of the printing using the toner. This fact, in addition to the larger electrified charge per unit area of the smaller toner particles, involves a phenomenon that the smaller toner particles are more used in development in the initial stage of the printing compared to the larger toner particles whereas the larger toner particles are more used with the progress of printing.
Accordingly, the resultant printed matter obtained in the initial stage has a sharp image and a low image density, and has a less sharp image and a higher image density with the progress of printing. Thus, uniform image quality is not obtained in the printed matter from the non-magnetic toner.